Microwave wide-band detectors



Nov. 14, 1967 TOSHIO AOKl I 3,353,125

MICROWAVE WIDE-BAND DETECTORS Filed June 4, 1965 2 Sheets-Sheet 1 4 f 4 I E I 3 lbVi'I/TOZ Tull/o 1904.0

BY 4L7 9 I ATTORNEY Nov. 14, 1967 TOSHIO AOKI 2 MICROWAVE WIDEBAND DETECTORS Fi led June 4, 1965 2 Sheets-Sheet 2 ATTORNEY United States Patent O 3,353,125 MICROWAVE WIDE-BAND DETECTORS Toshio Aoki, Kodaira-shi, Japan, assignor to Hitachi Electronics Company, Ltd., Tokyo, Japan, a corporation of Japan Filed June 4, 1965, Ser. No. 461,307 Claims priority, application Japan, Sept. 15, 1964, 39/ 52,397 2 Claims. (Cl. 333-98) This invention relates to microwave wave-band detectors.

The primary object of the present invention is to provide an microwave wide-band detector simple in construction and easy for maintenance.

Another object of the present invention is to provide a microwave wide-band detector which does not require movable adjusting element that would cause transmission loss and error in power measurement.

There are other objects and particularities of the present invention, which will be made obvious from the following detailed description, with reference to the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a conventional thermistor power meter;

FIG. 2 shows a longitudinal section of the same;

FIG. 3 is a perspective view of a conventional thermistor power meter;

FIG. 4 is a similar view of a conventional barretter power meter;

FIG. 5 is a cross-sectional view of a thermistor power meter embodying the present invention;

FIG. 6 shows a longitudinal section of the same;

FIG. 7 shows a cross-section of a barretter power meter embodying the present invention;

FIG. 8 shows a longitudinal section of the same;

FIGS. 9 and 10 are sectional views of a crystal detector embodying the present invention;

FIG. 11 is a Smith chart showing an example of input impedance characteristics as obtained by the present invention; and

FIG, 12 shows another embodiment of the invention as applied to power detector.

Referring to FIGS. 1 and 2, the thermistor power meter shown is for detecting electro-magnetic waves in microwave region, and comprises a wave guide 1, and a thermistor 4 with its opposite electrodes supported by conductors 2 and 3. The input electric field E is incident thereto in the direction parallel to that in which the thermistor 4 is mounted.

Thermistor power meter or barretter power meter of such a construction is well-known, and the principle of power measurement thereby is as described below.

Referring to FIGS. 3 and 4, if an electric field is applied to thermistor 5 or barretter 6 as the detecting element, change in resistance takes place as below.

In the case of thermistor,

B T+PC 1 where R =resistance value of thermistor, T=ambient temperature of thermistor, P=power consumed in thermistor,

B, C, J =constants inherent in thermistor, e=base of the natural logarithm.

In the case of barretter,

where R =resistance value of barretter, when power is applied thereto,

R =cold resistance of bar-retter,

P=power consumed by barretter,

T= ambient temperature,

J, n, C=constants inherent in barretter.

As are seen from Equations 1 and 2, Operating resistance values of the power detecting elements change in accordance with input power. Consequently, if a bridge circuit is constructed with such a detecting element forming one side thereof, the output voltage due to unbalance of the circuit represents the change in resistance of the detecting element or change in the input power. However, as is understood from Equations 1 and 2, when electric power is measured by the detecting element, the true power is not measured, if all the incident power is not consumed in the detecting element, but partly reflected therefrom. This necessitates impedance matching for power detection.

On the other hand, conventional thermistor or barretter power meter, as shown in FIGS. 1 to 4, changes coeflicient of reflection remarkably in accordance with the frequency of incident power, and in order to obtain correct measurement of power, an impedance matching adjustor must be provided directly before the power meter. Such an adjustor is required to be operated at each time when the frequency is changed. This is troublesome work, In addition, the provision of movable adjusting element causes transmission loss and error in power measurement. For example, the provision of adjustor above 50 go. band frequently leads to insertion loss of 0.4 db or so, and the error due to such a loss is near to 9%. By this reason, particularly in short wave region, such as millimeter-wave region, movable adjusting element is not provided, but instead, power detector is required to provide for impedance matching over a wide frequency band. For this purpose, certain improvements in arrangements shown in FIGS. 1 to 4 are known proposed, but any of them is not easy in construction, and extremely high skill is required for mounting of detecting element. This invention has succeeded to eliminate such disadvantages and to provide microwave detectors superior in operation as well as in maintenance.

Referring to FIGS. 5 and 6, the thermistor power meter shown and embodying the present invention comprises a wave guide 7, and an electrode bar 9 projecting thereinto from its finishing end wall 8 for a length of odd-number times about one fourth of the wave-length in the guide Ag, in the direction of propagation of electromagnetic waves towards the oscillation source, as oneend electrode of thermistor 10. The other electrode bar 11 is positioned at the point distant from the end 8 by a length of odd-number times about one fourth of the wave-length in the guide and extends in the direction parallel to the electric field and at right angle to the electrode bar 9, and serves as the other electrode of thermistor 10. FIGS. 7 and 8, a barretter 12 is used in place of thermistor. Electric analysis with such constructions has not yet been clarified enough, but experiments effected in 34 gc. frequency band have shown that impedance characteristics of extremely wide frequency band, such as VSWR of lower than 1.8 over the whole range of the wave guide-WRJ-32O or RG-96/u as wide as 26.5 to 40 go. is obtained, as shown in FIG. 11. Detective efiiciency of electric power is also superior and as high as In addition, if the electrodes to which is secured the detective element are covered by dielectrics surrounding the electrodes, the degree of concentration of electric field to the portion of detecting element is improved, and the wide-band feature is found further promoted.

The present invention can also be worked with crystal detectors. Thus, in FIGS. 9 and 10, the arrangement shown therein comprises electrodes 15 and 16 arranged in the manner similar to those shown in the preceding figures, and a detecting element consisting of whisker 13 and semi-conductor crystal 14 in series, and inserted between the electrodes.

If the portion of electrode mount 17 is constructed separately and connected to the wave guide tube 18 as shown in FIG. 12, the portion 17 which is composed of finishing end wall 8, electrode bars 9, 11, and detecting element 10, can be worked and mounted with extreme case and simplicity.

What is claimed is:

1. A microwave detector in a wave guide havin a fixed finishing end comprising a first elongated metal electrode having a length of odd-number times about one fourth of a wavelength in the guide, said first elongated metal electrode being secured to the finishing end of the wave guide and extending in a direction parallel to that of electric wave propagation from the finishing end of said wave guide towards the generator, 2. second elongated metal electrode disposed within said waveguide in a position distant from said finishing end of the wave guide towards the. generator by a length of oddnumber times about one fourth of the wave-length in the guide, said second elongated metal electrode being electrically insulated from the walls of the wave guide, and being disposed in a direction extending at a right angle to the first elongated metal electrode and parallel to the high frequency electric field, and a microwave detecting element secured between the free ends of the first and second elongated metal electrodes.

2. The microwave detector according to claim 1 in which both of said electrodes are covered by dielectrics surrounding the same.

References Cited FOREIGN PATENTS 755,532 2/1953 Germany.

HERMAN KARL SAALBACH, Primary Examiner.

L. ALLAHUT, Assistant Examiner. 

1. A MICROWAVE DETECTOR IN A WAVE GUIDE HAVING A FIXED FINISHING END COMPRISING A FIRST ELONGATED METAL ELECTRODE HAVING A LENGTH OF ODD-NUMBER TIMES ABOUT ONE FOURTH OF A WAVE-LENGTH IN THE GUIDE, SAID FIRST ELONGATED METAL ELECTRODE BEING SECURED TO THE FINISHING END OF THE WAVE GUIDE AND EXTENDING IN A DIRECTION PARALLEL TO THAT OF ELECTRIC WAVE PROPAGATION FROM THE FINISHING END OF SAID WAVE GUIDE TOWARDS THE GENERATOR, A SECOND ELONGATED METAL ELECTRODE DISPOSED WITHIN SAID WAVEGUIDE IN A POSITION DISTANT FROM SAID FINISHING END OF THE WAVE GUIDE TOWARDS THE GENERATOR BY A LENGTH OF ODDNUMBER TIMES ABOUT ONE FOURTH OF THE WAVE-LENGTH IN THE GUIDE, SAID SECOND ELONGATED METAL ELECTRODE BEING ELECTRICALLY INSULATED FROM THE WALLS OF THE WAVE GUIDE, AND BEING DISPOSED IN A DIRECTIO EXTENDING AT A RIGHT ANGLE TO THE FIRST ELONGATED METAL ELECTRODE AND PARALLEL TO THE HIGH FREQUENCY ELECTRIC FIELD, AND A MICROWAVE DETECTING ELEMENT SECURED BETWEEN THE FREE ENDS OF THE FIRST AND SECOND ELONGATED METAL ELECTRODE. 